Method for making a hybrid casting and forging stainless steel product

ABSTRACT

A method for making a hybrid casting and forging stainless steel product includes a) casting a stainless steel to form a cast billet, b) heat forging the cast billet to eliminate micro-shrinkage pores and gas holes produced in the cast billet during the casting process so as to form a forged element having a compact structure, and c) performing a solution treatment on the forged element to form a hybrid casting and forging stainless steel product. Thus, the hybrid casting and forging stainless steel product has mechanic specifications similar to that of the forged element by the forging process and the solution treatment, so that the stainless steel product has greater mechanic features and lower price, thereby enhancing the quality of the stainless steel product, and thereby decreasing costs of fabrication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for making a stainless steelproduct and, more particularly, to a method for making a hybrid castingand forging stainless steel product.

2. Description of the Related Art

A metallic working process is used to work a metallic material, such asthe stainless steel or the like, to form a worked metallic product. Theconventional metallic working process comprises a casting process and aforging process.

The casting process forms the worked metallic product at the liquidstate so that the cast metallic product is formed easily. Thus, thecasting process can be used to make a metallic product having acomplicated shape. In addition, the cast metallic product approaches thefinal shape and size to save the material and to reduce the workingcost. In addition, the casting process can use waste melting to reducethe cost of material. In addition, the noil produced by the castingprocess can be recycled to reduce the cost of material. In addition, thedie of the casting process has a cheaper price to reduce the cost offabrication. However, the metallic product worked by the casting processhas greater crystal grain sizes, so that the cast metallic product hasworse mechanic features. In addition, the cast metallic product easilyproduces gas holes and micro-shrinkage pores to reduce the relativedensity of the cast metallic product, so that the cast metallic producthas worse mechanic features and leakproof effects. In addition, thecasting process consumes the energy greatly.

The forging process forms the worked metallic product at the solidstate. Thus, the metallic product worked by the forging process hassmaller crystal grain sizes, so that the forged metallic product hasbetter mechanic features. In addition, the forged metallic product doesnot produce gas holes and micro-shrinkage pores to increase the relativedensity of the forged metallic product, so that the forged metallicproduct has better mechanic features and leakproof effects. However, theforging process forms the worked metallic product at the solid state sothat the forged metallic product is not formed easily. Thus, the forgingprocess cannot be used to make a metallic product having a complicatedshape. In addition, the forging process needs multiple working steps anddies, thereby increasing the cost of fabrication. In addition, the dieof the forging process has a more expensive price to increase the costof fabrication. In addition, the forging process uses rolled forgingmaterial having greater price, thereby increasing the cost of material.

In conclusion, the metallic product worked by the casting process has alower price. However, the metallic product worked by the casting processhas a worse quality. On the other hand, the metallic product worked bythe forging process has a better quality. However, the metallic productworked by the forging process has a greater price.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a method formaking a hybrid casting and forging stainless steel product comprises a)casting a stainless steel by a casting process to form a cast billet, b)heat forging the cast billet by a forging process to eliminatemicro-shrinkage pores and gas holes produced in the cast billet duringthe casting process so as to form a forged element having a compactstructure, and c) performing a solution treatment on the forged elementto form a hybrid casting and forging stainless steel product havingmechanic specifications similar to that of the forged element.

The primary objective of the present invention is to provide a methodfor making a hybrid casting and forging stainless steel product, whereinthe method combines the advantages of the casting and forging workingprocesses to produce a hybrid casting and forging stainless steelproduct having a lower price and a better quality.

Another objective of the present invention is to provide a method formaking a stainless steel product, wherein the stainless steel is workedby a casting process to form a cast billet to reduce the cost offabrication, the cast billet is then worked by a forging process toincrease the strength of the cast billet to form a forged element, andthe forged element is finally performed by a necessary heat treatment toform a hybrid casting and forging stainless steel product that combinesthe advantages of the casting and forging working effects so as toreduce the price and increase the quality.

A further objective of the present invention is to provide a method formaking a stainless steel product, wherein the hybrid casting and forgingstainless steel product has mechanic specifications (such as themechanic strength) similar to that of the forged element by the forgingprocess and the solution treatment, so that the stainless steel producthas greater mechanic features and lower price, thereby enhancing thequality of the stainless steel product, and thereby decreasing costs offabrication.

A further objective of the present invention is to provide a method formaking a stainless steel product, wherein the hybrid casting and forgingstainless steel product saves the material consumption and the workingsteps and reduces the energy loss.

Further benefits and advantages of the present invention will becomeapparent after a careful reading of the detailed description withappropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a comparison graph of a load curve of a method for making ahybrid casting and forging stainless steel product in accordance withthe preferred embodiment of the present invention.

FIG. 2 is a comparison graph of an elongation of the method for making ahybrid casting and forging stainless steel product in accordance withthe preferred embodiment of the present invention.

FIG. 3 is a comparison graph of a yield stress of the method for makinga hybrid casting and forging stainless steel product in accordance withthe preferred embodiment of the present invention.

FIG. 4 is a comparison graph of a tensile stress of the method formaking a hybrid casting and forging stainless steel product inaccordance with the preferred embodiment of the present invention.

FIG. 5 is a comparison graph of a hardness of the method for making ahybrid casting and forging stainless steel product in accordance withthe preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, a method for making a hybrid casting andforging stainless steel product in accordance with the preferredembodiment of the present invention comprises a) casting a stainlesssteel by a casting process to form a cast billet, b) heat forging thecast billet by a forging process to eliminate micro-shrinkage pores andgas holes produced in the cast billet during the casting process so asto form a forged element having a compact structure, and c) performing asolution treatment on the forged element to form a hybrid casting andforging stainless steel product having mechanic specifications similarto that of the forged element.

In the preferred embodiment of the present invention, the cast billet istreated by the forging process at a forging temperature of about 1000°C. to 1100° C. In addition, the upset ratio (h/h0) between the castbillet and the forged element is about 0.25 to 0.75 so that the castbillet has determined deformation and flow during the forging process.In addition, the forged element is treated by the solution treatmentduring two hours at a temperature of about 1100° C.

The features of the method of the present invention are described asfollows.

First of all, the hybrid casting and forging technology includes forminga cast billet having a similar shape by a casting process, and thenforging the cast billet to form a hybrid casting and forging product. Insuch a manner, the hybrid casting and forging technology uses a castelement formed by waste melting without having to use an expensivebar-shaped material. In addition, the cast billet has enhanced featuresafter the cast billet is forged to satisfy the specifications requiredby the forged element. In addition, the product having a complicatedshape can be cast previously to reduce the forging working steps. Inpractice, the hybrid casting and forging technology needs to build adatabase of the hybrid casting and forging procedure. The conventionalforging technology uses rolled forging material which has a smallercrystal grain size and a greater relative density, and the conventionalcasting technology uses casting material which has a greater crystalgrain size (with tree shaped crystalline) and a smaller relativedensity, and contains micro-shrinkage pores and gas holes, so that theforging features of the casting material are different from that of therolled forging material. Thus, the hybrid casting and forging technologyneeds to establish the relationship between the upset ratio, the forgingtemperature, the solution treatment and the mechanic specificationsunder the casting state to determine the optimum casting and forgingconditions so as to build a complete database of the hybrid casting andforging procedure. In such a manner, the casting and forging conditionsare combined by the database of the hybrid casting and forgingprocedure. For example, the database of the hybrid casting and forgingprocedure is based on the popular SUS304 stainless steel to functions asthe technology interface of the hybrid casting and forging technology.

Next, it is necessary to choose a casting and forging product havingproper size and shape. Then, by the database of the hybrid casting andforging procedure, the upset ratio is determined according to therequirement of the forged product. Then, a proper cast billet is formedby a casting process. Then, the cast billet is forged according toproper conditions, such as the forging temperature, forging pressure orthe like, to form a product billet. Then, the product billet samples aretreated by tests of the mechanic specification and the metallographicorganization and are compared with the data stored in the database ofthe hybrid casting and forging procedure. Finally, the product billet isperformed by a mechanic working process to form a hybrid casting andforging product.

The procedures of the complete hybrid casting and forging stainlesssteel product are described as follows.

First of all, it is necessary to establish the parameter database of thehybrid casting and forging stainless steel product, wherein the upsetratio (h/h0) is about ¾, ⅔, ½, ⅓and ¼, the forging temperature of thestainless steel cast element is about 1000° C. and 1100° C., and theheight of the cast billet is about 20 mm and 50 mm. In addition, afterthe testing sample is forged, the testing sample is performed by asolution treatment to judge the difference between the mechanic featuresof the testing sample before and after the solution treatment isperformed. The temperature of the cast billet is increased at about 200°C. to 300° C. per hour during the heat forging process. The heatconductive coefficient of the stainless steel is smaller than that ofthe low carbon steel or the low alloy steel, so that the stainless steelhas a longer heating period. In addition, the stainless steel cannot bekept too long under the forging temperature, so that the stainless steelis taken out immediately when the temperature of the stainless steelbillet is uniform to be forged. In addition, the temperature of the dieis kept at about 200° C. to 300° C. to decrease the temperaturedifferential between the cast billet and the die so as to eliminate theexperimental error. In addition, the forged element is cooled rapidly(the cooling speed is about 2° C./sec) after the heat forging process toprevent the feature of the forged element from being changed.

In fabrication, the cast billet is heated during 30 to 50 minutesaccording to the preset experimental parameters. Then, the cast billetis taken out rapidly and is placed onto the die to be forged. At thistime, the cast billet cannot be placed onto the die too long to preventthe die from being annealed and softened and to enhance the lifetime ofthe die. In addition, the die is heated to the temperature of about 200°C. to 300° C. to prevent the bulk material from producing a chillingeffect. Then, the forged element of taken out and is placed into thewater to be cooled. The experiment uses two groups of testing samples,wherein the testing sample (the forged element) of the first group isnot performed by any treatment after the cooling process, and thetesting sample of the second group is treated by the solution treatmentduring two hours at a temperature of about 1100° C. Then, the mechanicfeatures of the testing samples are tested as shown in FIGS. 1-5 tocompare the difference between the mechanic features of the testingsamples before and after the solution treatment is performed under theconditions of different upset ratios and forging temperatures so as tobuild a complete parameter database of the procedure of the completehybrid casting and forging stainless steel product. Then, by thedatabase, the corresponding parameters of the procedure are takenaccording to the required mechanic strength to facilitate forging thestainless steel product.

Thus, according to the experimental results, after the cast billet isforged and performed by the solution treatment, the hybrid casting andforging stainless steel product has mechanic specifications similar tothat of the forged element. In the preferred embodiment of the presentinvention, the forging temperature is about 1000° C. to 1100°, the upsetratio (h/h0) is about 0.25 to 0.75, and the solution treatmenttemperature is about 1100° C.

Accordingly, the stainless steel is worked by a casting process to forma cast billet to reduce the cost of fabrication, the cast billet is thenworked by a forging process to increase the strength of the cast billetto form a forged element, and the forged element is finally performed bya necessary heat treatment to form a hybrid casting and forgingstainless steel product that combines the advantages of the casting andforging working effects so as to reduce the price and increase thequality. In addition, the hybrid casting and forging stainless steelproduct has mechanic specifications (such as the mechanic strength)similar to that of the forged element by the forging process and thesolution treatment, so that the stainless steel product has greatermechanic features and lower price, thereby enhancing the quality of thestainless steel product, and thereby decreasing costs of fabrication.Further, the hybrid casting and forging stainless steel product savesthe material consumption and the working steps and reduces the energyloss.

Although the invention has been explained in relation to its preferredembodiment(s) as mentioned above, it is to be understood that many otherpossible modifications and variations can be made without departing fromthe scope of the present invention. It is, therefore, contemplated thatthe appended claim or claims will cover such modifications andvariations that fall within the true scope of the invention.

1. A method for making a hybrid casting and forging stainless steelproduct, comprising: a) casting a stainless steel by a casting processto form a cast billet; b) heat forging the cast billet by a forgingprocess to eliminate micro-shrinkage pores and gas holes produced in thecast billet during the casting process so as to form a forged elementhaving a compact structure; and c) performing a solution treatment onthe forged element to form a hybrid casting and forging stainless steelproduct having mechanic specifications similar to that of the forgedelement.
 2. The method in accordance with claim 1, wherein the castbillet is treated by the forging process at a forging temperature ofabout 1000° C. to 1110° C.
 3. The method in accordance with claim 1,wherein the upset ratio (h/h0) between the cast billet and the forgedelement is about 0.25 to 0.75 so that the cast billet has determineddeformation and flow during the forging process.
 4. The method inaccordance with claim 1, wherein the forged element is treated by thesolution treatment during two hours at a temperature of about 1100° C.